The term “marine farming” is used to refer to the breeding of marine fauna under controlled conditions in confined spaces. Confinement of the fauna tends to simplify the supply of nutrients and other requirements, as well as waste removal.
Several types of confined habitats for cultivating fish and other aquatic fauna are known. One type of system for breeding and rearing aquatic animals uses extensive ponds. Other breeding systems retain the animals in a chamber submerged in a body of water such as an off-shore site in a river, lake or sea. In open chambers, also known as “cages” and “flow through systems”, ambient water flows through the chamber providing oxygen and nutrients to the confined organisms, while at the same time removing waste products.
Closed systems have a chamber made from a water impermeable material. The chamber is filled with water and other substances which are thus separate from the surrounding environment. Closed chambers, also known as “recirculated aquaculture systems” (RAS), allow the composition of the chamber to be designed as required for the specific fauna being bred. In these chambers, nutrients, oxygen and other required substances must continuously be delivered into the chamber and waste products must be continuously removed or otherwise neutralized. During the fattening stage of growth, for example, the amount of nutrients delivered to fish should be proportional to the biomass density. Typically the daily nutrient mass is around 1.5% of the biomass. The amount of nutrients provided will determine the amount of toxic waste, such as ammonia and other nitrogenous compounds, CO2, and solid waste, released by the organisms. The amount of nutrients provided, as well as and other factors such as temperature, will also determine the oxygen requirement.
There are many known approaches and engineering methods for RAS systems that can be used in order to create the breeding conditions that optimize the output of the system.
In order to minimize costs and volume of these engineering R.A.S treatment systems, a water intake/water replacement system is employed that typically replaces about 10%-30% of the water in the tank with fresh water every day. Water replacement adds costs to the maintenance of the system as it adds to the energy costs especially when the added water is not at the optimum temperature and has to be heated or cooled. Water replacement can also create environmental problems. Thus, there are RAS systems that utilize complete water recycling, and do not add any fresh water to the tank.
Closed systems have associated life support systems that maintain optimal inside the chamber with respect to such parameters as temperature, nutrient composition, waste removal, biomass density, pH and oxygen concentration. The magnitude of the life support systems is determined to a large extent by the amount of nutrients added per day and the rate of water replacement.
Both open and closed systems protect the confined organisms from predators. Open cages have the advantage that oxygen does not have to be supplied exogenously if the biomass densities are not too intensive. Biomass densities of up to around 30 kg per cubic meter of water can usually be maintained in open systems without the need to supply exogenous oxygen. In open systems, toxic byproducts are flushed out, which is another advantage of open systems. On the other hand closed systems have the advantage that conditions inside the chamber, for example, water temperature, pH, and the water composition can be controlled as desired, while protecting the environment. Closed systems also protect the organisms from detrimental environmental factors such as toxins, pollution, and pathogens. Furthermore, higher biomasses are typically attainable in closed systems as opposed to open systems.
U.S. Pat. No. 4,205,625 to Muller-Feuga discloses a chamber for breeding and raising marine animals The chamber is composed of a flexible film which is inert with respect to a marine environment. A pump introduces water under a pressure greater than the surrounding environment into the chamber, and discharge openings are provided through which the water discharges.
U.S. Pat. No. 4,936,253 to Otamendi-Busto discloses a marine fish farm including a submersible cultivation cage and ballast tanks, and a tower, in which maintenance and personnel facilities are located. The depth of the cultivation cage is adjusted by the ballast tanks so that the cage is always below the level of influence of sea waves.
U.S. Pat. No. 5,762,024 to Meilahn discloses an aquaculture system having a rigid-walled floating tank that is positioned in a body of water. Water is provided to the tank via a floating pump assembly that is positioned in the body of water external to the tank. An inlet of the pump assembly is movable and may be positioned in a desired location and depth of the body of water, such that clean water that is free of surface contaminants and that is at a selected temperature is provided to the tank.